The present invention relates broadly to implement handles. More particularly, the present invention relates to an improved handle for utility knives which is adapted to fit the natural contours of the human hand to reduce strain and risk of injury. The invention is believed best classified in U.S. utility class 16, subclass 110R. The most pertinent prior art is found in class 16, Digest 19.
As will be appreciated, a variety of muscles in the hand and forearm must be employed for manipulation of a utility knife. The muscles of the forearm include the flexor digitorum profundus and flexor digitorum superficialis, which extend from the elbow into the length of the fingers. The flexor digitorum profundus terminates in four tendons, which enter the hand beneath the transverse carpal ligament. Four small muscles, known as the lumbricals, are connected with the tendons of the flexor digitorum profundus in the palm.
The flexor pollicis longus and flexor pollicis brevis extend the length of the forearm between the biceps and the wrist and into the length of the thumb. The pronator quadratus is associated with the wrist. Action of the wrist is controlled by motion of the flexor carpi ulnaris and a band of muscle which encircles the wrist, known as the flexor carpi radialis.
In the hand, the extensor pollicis longus and extensor pollicis brevis extend from the wrist into the thumb. The adductor pollicis longus and adductor pollicis brevis span the base of the fingers and bridge the fingers with the thumb. The flexor pollicis extends between the thumb and the wrist. Finger movement is generally controlled by the flexor pollicis brevis, associated with the thumb, and the opponens digiti minimi, flexor digiti minimi and abductor digiti minimi, which are associated with the fifth metacarpal of the hand.
The flexor digitorum superficialis flexes the second phalanx of each finger, the first phalanx at the metacarpophalangeal joint, and the hand at the wrist joint. It is supplied by branches of the median nerve. The flexor digitorum profundus is the most powerful of the forearm muscles. It flexes the terminal phalanx of each finger, the other phalanges, and the hand. It is supplied by the median nerve and a branch of the ulnar nerve. The tendons associated with the muscles of the hand and forearms comprise fibrous tendon sheaths. The base of the hand includes the muscles of hypothenar eminence, generally associated with the little finger, and the muscles of thenar eminence, generally associated with the thumb. The two latter muscle groups are bridged by the flexor retinaculum which forms the base of the palm.
As will be appreciated by those familiar with the meat processing industry, utility knives are used by various line workers to cut meat into packaging portions. Numerous repetitive cutting motions are required. For example, a typical line worker in the poultry industry will make in the order of fifteen thousand cuts per working day. When the hand is tightly clasped, as when a knife is firmly grasped, the muscles of the hand remain in tension and the flexor digitorum is tightly compressed. The muscles compress the radial artery and hinder circulation to the fingers. During a cutting operation, the line worker must intermittently grab and release the knife handle and must apply both forward and backward pulling motions to effectuate a sawing or slicing motion.
Conventional utility knives may include elongated, flattened handles with finger grips defined on the lower portion. Such knife handles typically include a planar shield at the forward end which separates the handle from the blade of the knife and provides the worker a pushing surface to facilitate sawing. The rearward end of the handle typically includes a downwardly extending flange which provides a pulling surface and prevents the knife from inadvertently slipping from the workers' hand.
Such conventional knife handles must be firmly grasped in the worker's clasped hand and retained in position by the fingers. It is imperative that the worker maintain a tight grip on the handle while manipulating the knife to deliver adequate cutting force to the blade. The complex musculature and nerves of the cutting hand are heavily taxed by the repeated impacts which result during cutting. With such conventional handles, force is experienced mainly at the base of the fingers. Additionally, blood circulation to the hand and fingers is greatly restricted when the hand remains in a tightly clasped position. Thus, continual use of such conventional utility knives often causes a great deal of discomfort and may result in permanent injury to the worker's hand. Disorders such as carpal tunnel syndrome and tendonitis are commonly caused by repetitive impact such as is experienced by the poultry line worker.
Hence it would be desirable to provide an ergonomic utility handle which could be easily and comfortably retained in the worker's relaxed hand without undue strain and without constriction of blood vessels or nerves.
In the prior art known to me, a variety of contoured implement handles have been suggested. For example, the tool handle disclosed by Bennett, U.S. Pat. No. 4,038,719, issued Aug. 2, 1977, includes an elongated shaft having a tapered end portion which is angled to fit into the worker's hand. The handle relieves strain and tension experienced by the worker during use, because the worker's wrist and forearm remain in a relaxed position. U.S. Pat. No. 4,617,697 issued to David on Oct. 21, 1986 discloses a deformable jacket adapted to be fitted about an implement handle to conform to the contours of the worker's hand.
The knife handle disclosed by Hoffman in U.S. Design Pat. No. D287,042, issued Dec. 2, 1986, includes a handle body of semi-arcuate configuration. The contoured butt portion of the handle body extends angularly downwardly. The forward end defines a receptacle for the knife blade which flares outwardly at the top and bottom to shield the worker's hand from the knife blade. The upper edge is notched to provide an improved grip.
The most relevant prior art known to me is U.S. Pat. No. 4,161,051, issued to Brodwin on July 17, 1979. The contoured handle disclosed therein includes corresponding curved portions adapted to fit comfortably within the palm of the worker's hand. The forward end of the handle rests upon the worker's thumb and creates a generally L-shaped rest for the fingers. The rearward end of the handle is adapted to wrap about the user's thumb and rest generally against the flexor pollicis brevis.
None of the prior art contoured handles known to me provide adequate support for the thumb to assist the worker to perform continual sweeping, sawing, or cutting motions required to cut poultry meat for packaging. Moreover, the prior art fails to teach adequate grip means which permit unobstructed free blood circulation and nerve conduction to the hands. Finally, the prior art handles known to me suggest no means for permitting the worker's hand to intermittently grip the handle and relax the grip without releasing the knife altogether.